A high-resolution genetic signature of demographic and spatial expansion in epizootic rabies virus

Abstract

Emerging pathogens potentially undergo rapid evolution while expanding in population size and geographic range during the course of invasion, yet it is generally difficult to demonstrate how these processes interact. Our analysis of a 30-yr data set covering a large-scale rabies virus outbreak among North American raccoons reveals the long lasting effect of the initial infection wave in determining how viral populations are genetically structured in space. We further find that coalescent-based estimates derived from the genetic data yielded an amazingly accurate reconstruction of the known spatial and demographic dynamics of the virus over time. Our study demonstrates the combined evolutionary and population dynamic processes characterizing the spread of pathogen after its introduction into a fully susceptible host population. Furthermore, the results provide important insights regarding the spatial scale of rabies persistence and validate the use of coalescent approaches for uncovering even relatively complex population histories. Such approaches will be of increasing relevance for understanding the epidemiology of emerging zoonotic diseases in a landscape context. invasion ͉ phylogeography ͉ Procyon lotor ͉ wildlife disease ͉ zoonoses

The Frequency of Fitness Peak Shifts Is Increased at Expanding Range Margins Due to Mutation Surfing

“…Deleterious mutations that arise on the edge of a shifting range can reach higher density and spatial extent than would be achieved in a stationary population. This is due to the mutation surfing phenomenon (Edmonds et al 2004;Klopfstein et al 2006;Biek et al 2007;Travis et al 2007) where lower-fitness genotypes, occurring by chance on the edge of the range, may colonize adjacent subpopulations and increase in abundance through a succession of founder effects. Lower-fitness individuals (aB/Ab) are usually outcompeted when the ancestral genotype (ab) has already reached fixation in subpopulations of a stationary range and away from the advancing front of dynamic ranges.…”

“…Ecological models indicate that habitat loss and climate change interact to determine extinction risk at the species level (Travis 2003) but, currently, an understanding of the synergistic effects of these two environmental drivers on genetic processes is lacking. A recent empirical study, demonstrating mutation surfing in the rabies virus (Biek et al 2007), has highlighted the importance of landscape structure effects on spatial genetic dynamics. Integrating population genetics and landscape ecology models would represent an important addition to recent developments in landscape genetics (Storfer et al 2007) and offer new insights into the biology of range expansions.…”

Rabies Virus in Raccoons, Ohio, 2004

“…We amplifi ed a 1,345-nt portion of the glycoprotein gene (G) and, for a smaller subset of samples (n = 20), the complete nucleoprotein gene (N) (1,416 nt,) (see [6] for primers and conditions). Sequences from a Florida raccoon (G, U27216; N, U27220) were included as an outgroup.…”

Innate immune responses in raccoons after raccoon rabies virus infection

“…In this study, we focused on the interaction between the raccoon strain of rabies virus (RRV) and its natural reservoir host, the raccoon (Procyon lotor), to gain a better understanding of innate immune responses triggered by virus infection. RRV was first noted in Florida around the 1940s where it remain localized until the late 1970s, when a second outbreak facilitated rapid spread along the eastern seaboard of North America (Biek et al, 2007). High densities of raccoons in urban and suburban areas (Totton et al, 2002) and the concomitant increase in potential human and pet exposures present a serious threat to human health.…”